| Hard Fun Co. Oy | Professional & scientific | 2025 |
| Hasu Holding Oy | Professional & scientific | 2022 |
| Hautauspalvelu Mikko Haakana Oy | Other services | 2026 |
| Hautaustoimisto ja Kukkakauppa Törrönen Ky | Other services | 1948 |
| Havanna Pizzeria Oy | Hospitality | 2022 |
| Havi Oy | Manufacturing | 1986 |
| Hei Palvelut OY | Administrative & support | 2022 |
| Heikki Vidman Oy | Hospitality | 2000 |
| Heinälampi-Yhtymä Oy | Real estate | 2004 |
| Heiskasen Kiinteistöt Oy | Real estate | 1989 |
| HelHug Oy | Construction | 1996 |
| Hietsun Venesäilytys Oy | Transport & logistics | 2003 |
| Hiitolanjoen Voima Oy | Energy | 1998 |
| HillWay Oy | Transport & logistics | 2024 |
| Hilpeät Varpaat Oy | Health & social care | 2022 |
| Hinausautot Purhonen Oy | Transport & logistics | 1986 |
| Hiuspalvelu Atlantis Oy | Other services | 2019 |
| Hockey Is My Life Oy | Construction | 2018 |
| Hoitava Solutions Oy | Information & communication | 2025 |
| Hoivatar Oy Lummea | Health & social care | 2012 |
| Hostel Krauze Oy | Administrative & support | 2015 |
| Hotelli Immalanjärvi Oy | Hospitality | 2013 |
| Hotelli Mehiläiset Oy | Real estate | 2023 |
| House & Marine Finland Oy | Hospitality | 2007 |
| Hui Hong Oy | Hospitality | 2019 |
| Hullu Kettu Oy | Hospitality | 2019 |
| Huoltamo Sipolainen Ky | Wholesale & retail | 1986 |
| Hydstahl Ky | Manufacturing | 1980 |
| Hyvi Oy | Health & social care | 2022 |
| Hyvinvoinnin Vuoksi Oy | Education | 2012 |
| IF Spedition Consulting Oy | Transport & logistics | 2009 |
| IG Oy Imatra | Arts & recreation | 2020 |
| IL-Majoitus Oy | Hospitality | 2008 |
| IMNO Oy | Real estate | 2021 |
| Imruscan OY | Professional & scientific | 2001 |
| IPV Reds Oy | Arts & recreation | 2024 |
| IS Hostels Oy | Hospitality | 2019 |
| Idan.fi Oy | Administrative & support | 2021 |
| Ideas Aduos avoin yhtiö | Professional & scientific | 2006 |
| Idän Kone ja Puu Oy | Manufacturing | 1994 |
| Iiva Oy | Wholesale & retail | 2010 |
| Ilmakuvaamo Taivas Oy | Professional & scientific | 2012 |
| Iloiset Leipurit Oy | Professional & scientific | 2023 |
| Ilyazov Oy | Hospitality | 2019 |
| Imantti Oy | Hospitality | 2017 |
| Imatel Roots Group Oy | Professional & scientific | 2021 |
| Imatra Booking Oy | Administrative & support | 2013 |
| Imatra FNW Oy | Energy | 2010 |
| Imatra Spirits Oy | Wholesale & retail | 2025 |
| Imatran Autokulma Oy | Other services | 2020 |
| Imatran Autopurkamo Oy | Wholesale & retail | 2022 |
| Imatran Betoniteräs Oy | Construction | 1994 |
| Imatran Bitumikate Oy | Construction | 2020 |
| Imatran Digiapu Oy | Information & communication | 2021 |
| Imatran Eläinklinikka Oy | Professional & scientific | 1987 |
| Imatran Fysioteekki Oy | Health & social care | 1987 |
| Imatran Hitsaus-Asennus Oy | Manufacturing | 1966 |
| Imatran Hotelliravintolat OY | Hospitality | 2020 |
| Imatran Immo Oy | Construction | 1997 |
| Imatran Insinööriniementien vesiosuuskunta | Water & waste | 2024 |
| Imatran Invataksipalvelu Lampinen Oy | Transport & logistics | 2006 |
| Imatran JK-Ravintola Oy | Hospitality | 2008 |
| Imatran Kalatalo Oy | Wholesale & retail | 2010 |
| Imatran Karhunpesä Avoin yhtiö | Hospitality | 2000 |
| Imatran Keilahalli Oy | Arts & recreation | 2019 |
| Imatran Kerho Oy | Arts & recreation | 1959 |
| Imatran Kesähotelli Oy | Hospitality | 2005 |
| Imatran Ketterä Oy | Arts & recreation | 2018 |
| Imatran Kiinteistö- ja Aluepalvelu Oy | Administrative & support | 2011 |
| Imatran Kiinteistö- ja asuntosijoitus Oy | Real estate | 2018 |
| Imatran Kiinteistöhallinto Oy | Real estate | 2024 |
| Imatran Kivikaiverrus Oy | Manufacturing | 1983 |
| Imatran Kivikide Ky | Real estate | 1984 |
| Imatran Kone Oy | Manufacturing | 2009 |
| Imatran Koneistuspalvelu Oy | Manufacturing | 2012 |
| Imatran Kotiapu Oy | Health & social care | 2015 |
| Imatran Kukka- ja Hautauspalvelu Pesonen Ky | Wholesale & retail | 1990 |
| Imatran Kylmäpalvelu Oy | Manufacturing | 1989 |
| Imatran Kylpylä Oy | Hospitality | 1985 |
| Imatran Kyytibussit Oy | Transport & logistics | 1993 |
| Imatran LVI-Asennus Oy | Construction | 2025 |
| Imatran LVIS-Kiinteistöt Oy | Real estate | 2022 |
| Imatran Laiva-Osakeyhtiö | Transport & logistics | 2025 |
| Imatran Lvi-Apu Oy | Professional & scientific | 2007 |
| Imatran Lämpö Oy | Energy | 2013 |
| Imatran Maatalouskonehuolto Ky | | 1988 |
| Imatran Mainoslahja Ky | Wholesale & retail | 2024 |
| Imatran Musiikki Oy | Wholesale & retail | 2008 |
| Imatran Nisse Oy | Hospitality | 2016 |
| Imatran Nuohouspalvelu Oy | Administrative & support | 2007 |
| Imatran Pelti- ja Rautaliike Oy | Construction | 1964 |
| Imatran Putkipalvelu Oy | Construction | 2001 |
| Imatran Puuntyöstöverstas Kymäläinen & Leinonen | | 1988 |
| Imatran Raja-Rakenne Oy | Construction | 1975 |
| Imatran Rantahovi Kommandiittiyhtiö | Hospitality | 1991 |
| Imatran Ruiskukka Oy | Real estate | 1987 |
| Imatran Ruosteenesto Oy | Other services | 1994 |
| Imatran Satupa Oy | Real estate | 1987 |
| Imatran Seudun Kehitysyhtiö Oy | Financial services | 1982 |
| Imatran Seudun Sähkö Oy | Energy | 1929 |